Here are the most important things to do if your child disappears:
Call 911 for the Police
Call the FBI (Yes, you the parent) - See Federal Government pages in your local phone directory
Call the Sheriff (Yes, you the parent)
Choose a Print Shop to meet volunteers
Tell local Radio Stations:
That your child is missing
At what print shop to meet to distribute posters
Tell local TV Stations immediately
Tell local Newspapers immediately
Call local Child Locator Services - See State Government pages (look under Health) and Community Services pages in your local phone directory
Call NCMEC - the National Center for Missing and Exploited Children (800) 843-5678 - Ask NCMEC to contact the FBI's Child Abduction and Serial Killer Unit as to whether or not their services would be appropriate.
Make sure child is registered in FBI's NCIC computer as "Stranger Abducted" if you believe it true.
Send out searchers (Local SAR groups with police leaderships)